Study of Thermal Aging Behavior of Epoxy Molding Compound for Applications in Harsh Environments

In the automotive industry, epoxy-based molding compounds (EMCs) are often used to protect not only single IC packages but also entire electronic control units (ECUs). The EMC undergoes thermal aging during the operation-lifecycle of its parent electronic package. The thermal aging oxidizes the EMC, which can alter its mechanical properties significantly. Understanding the oxidation phenomenon of EMC and its effect on property changes is critically required to predict the reliability of ECUs subjected to harsh environments. In this study, the oxidation phenomenon of EMC is characterized experimentally by measuring oxidation growth rate and the mechanical properties of oxidized EMC. In the first task, EMC samples are subjected to three different high temperature storage (HTS) conditions - 170 °C, 200 °C and 230 °C. The thicknesses of the oxidized layers are measured as a function of storage time (from 0 to 1500 hours) using a fluorescent microscope. The oxidation growth rates at the storage temperatures are determined from the thickness measurements, and they are subsequently used to determine the activation energy of the growth rate. In the second task, thin samples (300 μm thick) are subjected to a HTS condition until they are fully oxidized. Then, critical thermo-mechanical properties of oxidized EMC, including coefficient of thermal expansion (CTE), glass transition temperature, and modulus of elasticity, are measured using digital image correlation (DIC) and dynamic mechanical analysis (DMA), respectively. The detailed procedures of the experimental characterization are presented together with the test results. Their implications on the ECU reliability is also discussed.